All-wheel steering systems have been known and used for some time now. Examples of all-wheel steering systems are described in U.S. Pat. Nos. 5,607,028, 5,417,299, 5,217,083, and 5,111,901, all of which are entitled “All-Wheel Steering System,” and are hereby incorporated by reference. Some known all-wheel steering systems are purely mechanical, meaning that the rear wheel angle is determined by gears and gear ratios manually selected by the vehicle operator with the shift of a lever. Unfortunately, this type of all-wheel steering system adds considerable weight and complexity to the mechanical subsystem of the vehicle. Other all-wheel steering systems provide rear wheel steering independent of the front wheel angle. In this configuration, the operator steers the rear wheels independently of the front wheels. The rear wheels may be steered with a separate steering wheel, joy stick or potentiometer. This type of system is typically used on vehicles that are steered by two operators: one operator steers the front wheels and one operator steers the rear wheels. Unfortunately, the use of two operators has a number of disadvantages such as increasing the labor costs associated with operating the vehicle. Electronically controlled systems have also been employed.
All-wheel steering systems may be often used on larger vehicles such as trucks. It is desirable for these vehicles to be able to maneuver into small spaces in short periods of time. All-wheel steering provides great benefits in this regard because it provides a smaller minimum turning radius. All-wheel steering systems may also be used in other types of vehicles.
All-wheel steering systems, particularly those that are electronically controlled, typically implement steering algorithms to control steering of one or more sets of wheels. In order to provide flexibility in the types of steering algorithms that can be implemented, it is desirable to provide all-wheel steering systems with access to a variety of sources of vehicle data. It is also desirable in many instances to provide other electronic systems on-board the vehicle with access to data from the steering control system. What is needed is a control system architecture that provides an improved integration of the steering control system with other vehicle devices.
All-wheel steering systems typically have more modes of operation than a standard front wheel drive system. In order to allow a vehicle operator to use an all-wheel steer system most effectively, it is desirable to provide the operator with feedback regarding operation of the system including vehicle diagnostics. What is needed is improved systems for providing operator feedback in connection with a steering control system.
It is typically necessary to periodically calibrate the steering system of an all-wheel steering vehicle. Often these systems are difficult to calibrate and require the operator to get underneath the truck. What is needed is a steering control system that it is easier to calibrate.
Accordingly, there is an ongoing need for improvements to control systems and methods used in connection with such steering systems. It should be understood, however, that the techniques below extend to those embodiments which fall within the scope of the appended claims regardless of whether they meet any of the above-mentioned needs.